: This study aimed to explore the treatment modalities of relapsed osteosarcoma, treatment results, and prognostic factors.

: We conducted a retrospective study of patients treated for relapsed osteosarcoma between 2005 and 2019. Patient survival was compared according to age, performance status, time to relapse, and surgical treatment at the relapse. Values of p<0.05 were considered to indicate statistical significance.

: We included 49 patients who were treated for osteosarcoma. During the 13-year study period, 16 patients had relapsed osteosarcoma (32.7%). Prognostic factors of relapse were age over 18 years (p = 0.03), axial tumors (p = 0.01), and positive surgical margins (p = 0.018). Nine patients had palliative chemotherapy at the time of relapse. After a median follow-up of 8 months (range: 4–65 months), the overall survival at 1 year, 2 years, and 5 years after diagnosis of the relapse was 46.7%, 31.1%, and 20.7%, respectively. Relapsed osteosarcoma patients who had good performance status, late relapse (after 12 months), as well as surgery of the relapsed disease had better overall survival (OS).

: Surgical treatment of relapsed osteosarcoma should be performed whenever possible since it improves significantly the survival of patients. Good performance status and late relapse were also associated with better survival.